Interpretive Summary: Cotton crop biomass remaining in the field after mechanical seed cotton harvest has typically been left as residue on the soil surface, plowed back into the soil prior to the planting of the next crop, or used as animal feed. However, this material may be of additional value to biofuel processors and those producing bio-based composite materials; thus providing an additional revenue stream to cotton producers. This work was undertaken to quantify the amount of biomass produced by irrigated and non-irrigated cotton crops produced in the Southern High Plains region and provide data characterizing the attributes of the residual biomass left in the field after mechanical harvest. Crops were produced at three locations in the Southern High Plains and differed by irrigation practice and harvest method. Total dry-matter (DM) biomass produced at the Lubbock (sub-surface drip irrigated), Floyd (non-irrigated), and Dawson (center pivot irrigated) locations were 8643, 3227, and 6456 kg DM/ha, respectively. After mechanical seed cotton harvest, 3537 (41%), 1578 (49%), and 4210 (65%) kg DM/ha remained in the fields at the Lubbock (machine stripped), Floyd (machine stripped), and Dawson (machine picked) locations, respectively. Harvest index, a measure of the fraction of total biomass made up by lint and seed, averaged .47, .45, and .40 for the Lubbock, Floyd, and Dawson locations, respectively. Analysis of individual biomass components indicated that heating value was higher for stick (16.94 MJ/kg DM) and bur (17.10 MJ/kg DM) than other vegetative material (OVM) (14.38 MJ/kg DM). Lignin and cellulose content were also greater for stick and bur than OVM making them potentially more attractive to processors for bio-fuel and bio-based composite production. Additional analytical analysis indicated higher nitrogen, phosphorus, digestibility, and net energy for OVM than stick or bur, making OVM more attractive from a soil nutrient and animal feed standpoint. Regional estimates of biomass availability in the Texas Southern High Plains averaged about 609,000 and 180,000 tonnes for irrigated and non-irrigated cotton, respectively, over the five year period from 2008 - 2012. Cotton producers must consider costs associated with harvest, storage, and transportation of biomass materials but also costs associated with replacement fertilizer and reduced soil tilth prior to making the decision to remove residual cotton crop biomass for off-site use.

Technical Abstract:
Cotton crop residual biomass remaining in the field after mechanical seed cotton harvest is not typically harvested and utilized off-site thereby generating additional revenue for producers. Recently, interest has increased in utilizing biomass materials as feedstock for the production of fuel and composite materials. This work was undertaken to investigate the quantity and characteristics of residual biomass remaining in the field for cotton produced in the Southern High Plains of the US. Three growing locations were studied and varied with regard to irrigation use and application system, and harvest method. In order to differentiate the amount of biomass available before and after seed cotton harvest as well as the physical location of the material, biomass yield was measured for five collection groups: 1) pre-harvest stalk, 2) pre-harvest ground, 3) post-harvest stalk, 4) post-harvest ground, and 5) bur trial (for the two stripper harvested locations only). Within each collection group, the biomass was separated into four components: seed cotton, stick, bur, and other vegetative material (OVM). Total biomass produced at the Lubbock (sub-surface drip irrigated, machine stripped), Floyd (non-irrigated, machine stripped), and Dawson (center pivot irrigated, machine picked) locations were 8643, 3227, and 6456 kg DM/ha, respectively. After mechanical seed cotton harvest, 3537 (41%), 1578 (49%), and 4210 (65%) kg DM/ha remained in the fields at the Lubbock, Floyd, and Dawson locations, respectively. Heating value was higher for stick (16.94 MJ/kg DM) and bur (17.10 MJ/kg DM) than OVM (14.38 MJ/kg DM) which also had excessively high ash content. Lignin and cellulose content were greater for stick and bur than OVM making them potentially more attractive to processors for bio-fuel and bio-based composite production. Additional analytical analysis indicated higher nitrogen, phosphorus, crude and digestible protein, digestibility, and net energy for OVM than stick or bur, making OVM more attractive from a soil nutrient and animal feed standpoint. Harvestable residual biomass was estimated on a regional basis for five National Agricultural Statistics Service districts in Texas and averaged 609,000 and 180,000 tonnes for irrigated and non-irrigated cotton over the five year period from 2008 – 2012. Energy content of the harvestable biomass was similar on a mass basis (irrigated: 16.82 GJ/tonne vs. non-irrigated: 16.95 GJ/tonne) but on an area basis averaged 15.3 GJ/ha (4257 kW-h/ha) for irrigated and 4.87 GJ/ha (1353 kW-h/ha) for non-irrigated cotton. Cotton producers must consider costs associated with harvest, storage, and transportation of biomass materials but also costs associated with replacement fertilizer and reduced soil tilth prior to making the decision to remove residual cotton crop biomass for off-site use.